Accompanying recent popularization of computers, an inkjet printer is widely used for printing letters or an image on paper, film, cloth or the like not only at offices but also at homes.
The inkjet recording method includes a system of jetting out a liquid droplet by applying a pressure from a piezoelectric element, a system of jetting out a liquid droplet by generating a bubble in the ink under heat, a system of using an ultrasonic wave, and a system of jetting out a liquid droplet by suction using an electrostatic force. The ink used for such inkjet recording includes an aqueous ink, an oily ink and a solid (fusion-type) ink. Among these inks, an aqueous ink is predominating in view of production, handleability, odor, safety and the like.
The dye used in such an ink for inkjet recording is required to have high solubility in a solvent, enable high-density recording, provide good color hue, exhibit excellent fastness to light, heat, air, water and chemicals, ensure good fixing property to an image-receiving material and less bleeding, give an ink having excellent storability, have high purity and no toxicity, and be available at a low cost. However, it is very difficult to find out a dye satisfying these requirements in a high level. Various dyes and pigments for inkjet recording have been already proposed and actually used, however, a dye satisfying all requirements is not yet found out at present. Conventionally well-known dyes and pigments having a color index (C.I.) number can hardly satisfy both color hue and fastness required of the ink for inkjet recording.
The present inventors have continued studies on the inkjet ink using a dye so as to solve the above-described problems. Particularly, the aqueous inkjet ink is water-soluble and therefore, often suffers from low image durability. As for the ink suitable for aqueous inkjet recording, a heterocyclic group-containing azo dye having a specific structure is disclosed in JP-A-2002-371214 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) and a phthalocyanine dye having a specific structure is disclosed in JP-A-2003-3086, JP-A-2003-3099 and JP-A-2003-3109. From the standpoint of satisfying both color hue and fastness, these techniques have succeeded in providing an improvement. However, the inkjet recorded image is used in various indoor or outdoor environments and sometimes causes a phenomenon (so-called discoloration) that the fastness changes depending on the color tone of the image obtained. Particularly, in an image drawn by using two or more inks, even when the dye itself is fast, a fastness changing phenomenon occurs due to interaction resulting from mixing of dyes. In order to prevent occurrence of such a defect, more improvement is demanded.